1. Field of the Invention
The present invention relates to a microcomputer having a memory stored with a program beforehand, prepared at a user site, and more specifically to such a microcomputer where the test of an operation in accordance with programs stored in the memory can be performed.
2. Description of the related art
Up to this time, two types of tests are performed after microcomputers, having an internal read only memory (hereinafter abbreviated ROM) have finished or completed specific functions. Specifically, in a function test, the microcomputer is set in a test mode, and instructions are inputted from an external to an input port of the microcomputer, so that the output of the computer is compared with an expected value previously prepared. On the other hand, in a ROM content confirmation test, information is read out through an output port of the microcomputer from the ROM storing a program previously prepared at a user site (called "user's program" hereinafter), and the information thus read out is compared with an expected value which has previously been prepared on the basis of the user's program.
In the above mentioned function test, the external input instructions are prepared by microcomputer producers, and therefore, the sequences of instructions are inevitably limited in variety. Accordingly, a perfect function test cannot be expected. To the contrary, the user's program which are stored in ROMs have an indefinite variety. However, the ROM content confirmation test can examine only whether the user's program is properly stored in the ROM, and cannot confirm whether the microcomputer can properly operate on the basis of the user's program stored in the ROM. Because of this, although microcomputers have been regarded as being good from the result of the tests performed by the producer, when the microcomputers were actually assembled in systems or apparatus at the user side, the microcomputers often did not properly operate due to defects attributable to the combination of instructions.